距沙坑高7m处，以v0=10m/s的初速度竖直向上抛出一个重力为5N的物体，物体

如图所示，固定的凹槽水平表面光滑，其内放置U形滑板N，滑板两端为半径R=0.45m的1/4圆弧面．A和D分别是圆弧的端点，BC段表面粗糙，其余段表面光滑．小滑块P₁和P₂的质量均为m．滑板的质量M=4m，P₁和P₂与BC面的动摩擦因数分别为μ₁=0.10和μ₂=0.40，最大静摩擦力近似等于滑动摩擦力．开始时滑板紧靠槽的左端，P₂静止在粗糙面的B点，P₁以v₀=4.0m/s的初速度从A点沿弧面自由滑下，与P₂发生弹性碰撞后，P₁处在粗糙面B点上．当P₂滑到C点时，滑板恰好与槽的右端碰撞并与槽牢固粘连，P₂继续运动，到达D点时速度为零．P₁与P₂视为质点，取g=10m/s²．问：

（1）P₂在BC段向右滑动时，滑板的加速度为多大？

（2）BC长度为多少？N、P₁和P₂最终静止后，P₁与P₂间的距离为多少？

产生材料价格脱离标准的原因，可能会有（）。

A.进料数量未按经济订货量办理

B.折扣期内延期付款，未获优惠

C.购入低价材料

D.增加运输途中损耗

张某欲杀害周某，但又不想自己动手，遂将装好子弹的手枪交给赵某，并骗赵某说枪里是橡皮子弹，既不会打死人也不会伤人，但可以吓唬对方一下，赵某信以为真，遂向周某开枪，由于枪法不准，将周某身边的陆某打死。下列说法正确的是（）。

A.赵某构成过失致人死亡罪

B.张某和赵某成立共同犯罪

C.张某构成故意杀人罪（既遂）

D.张某构成故意杀人罪（未遂）

There is a difference between science and technology. Science is a method of answering (1) questions; technology is a method of solving practical problems. Science has to do with discovering the facts and relationships between (2) phenomena in nature and with establishing theories that (3) to organize these facts and relationships; technology has to do with tools, techniques, and (3) for applying the findings of science. Another (5) between science and technology has to do with the progress in each.

Progress in science (6) the human factor. Scientists, who seek to understand the universe and know the truth within the highest degree of (7) and certainty, cannot (8) their own or other people’s likes or dislikes or to popular ideas about the fitness of things. What scientists discover may shock or (9) people-as did Darwin’s theory of evolution. But even an unpleasant truth is (10) than likely to be useful; besides, we have the choice of refusing to believe it! But (11) so with technology; we do not have the choice of refusing to hear the sound produced by a supersonic aircraft flying overhead; we cannot refuse to breathe polluted air. (12) science, progress in technology must be measured (13) the human factor. The purpose of technology is to serve people—people (14) , not merely some people; and future generations, not merely those who presently wish to (15) advantage for themselves.

We are all familiar with the (16) use of technology. Many people blame technology itself (17) widespread pollution, resource depletion (枯竭) and even social decay in general—so much (18) the promise of technology is " (19) " That promise is a cleaner and healthier world. If wise applications of science and technology do not (20) a better world, what else will

5（）

A.implication

B. friction

C. discrimination

D. distinction

可燃气体检测仪报警（高限）设定值应小于或等于可燃气体爆炸下限浓度（以体积百分数表示）值的25%。